Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Need to turn off unused lights?

Learn more physics!

Most recent answer: 10/22/2007
Q:
Do you really need to turn off unused lights in winter if you have electruc heat in your house? I mean suppose that you close the shades so that no light goes outside. Then, doesn’t all the electrucal energy you use wind up as heat anyway. Actually, anything electrucal.... just leave them all on... whether the thing is efficient or not, doesn’t all the energy it uses wind up as heat in your house eventually. What’s up with this? And it seems like this is still mostly true even if you have some other kind of heat in your house... except for the fact that gas-heat is sort-of cheaper than electruc
- Chris Leo III
A:
Chris,
You are right that most of the energy that goes into a light bulb will end up as heat somewhere in your house, but the key question is "where" that heat ends up.

If you feel the light bulb and the fixture that holds it you will certainly notice that it gets hot. The problem is that this is not necessarily doing much to heat the rest of the house. For example, if your light fixture is in the ceiling, heating the fixture will not do much to heat the air in the room since heat rises and the warmth generated by the light will tend to stay in (or near) the ceiling. Even a table lamp wont heat you very efficiently since it is not designed for the primary purpose of transferring heat to its surroundings (although it would be somewhat better than a ceiling light).

The bottom line is that you are better off turning off the light bulb and using the electricity you save to run a real heater which is carefully engineered to warm the air in the room.
MS

(published on 10/22/2007)

Follow-up on this answer.